Optical semiconductor devices such as light-emitting diode (LED) devices consume low power and have a long life. Moreover optical semiconductor devices can be used under harsh environments. For these reasons, optical semiconductor devices are used in a wide range of applications such as mobile phone backlight, liquid-crystal TV backlight, automobile lamps, lighting apparatuses, and signs.
When optical semiconductor elements (e.g. LED), which are light-emitting elements used in optical semiconductor devices are directly exposed to the atmosphere, the light-emitting performance of the optical semiconductor elements rapidly decreases due to moisture, floating dust, or the like in the atmosphere. To avoid this, such optical semiconductor elements are normally sealed with a sealant for an optical semiconductor device.
Patent Document 1 described below discloses an epoxy resin material including hydrogenated bisphenol A glycidyl ether, an alicyclic epoxy monomer, and a potential catalyst as a sealant for an optical semiconductor device. The epoxy resin material is cured by thermal cationic polymerization.    Patent Document 1: JP 2003-73452 A